Shadow mask of color CRT

ABSTRACT

The color cathode-ray tube includes a panel having a fluorescent screen formed on the inner surface thereof, a funnel coupled to the panel, an electron gun mounted into the neck portion of the funnel for emitting electron beams toward the fluorescent screen, and a shadow mask mounted on the fluorescent screen formed on the inner surface of the panel and having a predetermined distance from the fluorescent screen for carrying out color selection. The shadow mask is in a rectangular shape having a longer axis and a shorter axis and including a plurality of beam through apertures. The vertical pitch of the beam through apertures is between 0.15 mm and 0.35 mm. The vertical pitch of the beam through apertures increases as it goes from the central portion to the end portion of the shorter axis of the shadow mask.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a shadow mask having a vertical pitchthat simultaneously satisfies moire characteristic and puritycharacteristic, as distinguished from a conventional shadow mask havinga vertical pitch that is equal in the shorter axis direction thereof butdecreases as it goes along the longer axis direction thereof for tiltarray design.

2. Background of the Related Art

Referring to FIG. 1, a conventional color cathode-ray tube (CRT)includes a panel 1 having a fluorescent screen 4 with R, G, B colorscoated on the inner surface thereof and an explosion-proof glass fixedto the front portion thereof, a funnel 2 coupled to the rear panel 1,and an electron gun inserted in the neck portion of the funnel 2 foremitting electron beams 6. The color CRT further includes a deflectionyoke for deflecting the electron beams, a shadow mask 3 that is mountedon the inner side of the panel at a predetermined distance therefrom andhas a plurality of apertures through which the electron beams pass, anda frame 7 for fixing and supporting the shadow mask so as to maintainthe predetermined distance between the shadow mask and the inner surfaceof the panel. The color CRT also has a spring 8, an inner shield 9 forshielding the earth-magnetic field so as to prevent the CRT from beingaffected by the earth-magnetic field, and a reinforcing band 11 mountedto surround the side of the panel for protecting the CRT from eternalshock. In addition, the conventional color CRT includes a magnet 10 forcorrecting the electron beam path so as to allow the electron beams toaccurately hit predetermined phosphors, thereby preventing poor colorpurity.

FIG. 2 illustrates the structure of the conventional shadow mask. InFIG. 2, PVo denotes a vertical pitch between neighboring beams throughapertures formed at the central portion of the shadow mask and PVcdenotes a vertical pitch between adjacent beams through apertures placedat the corner portion of the shadow mask. Furthermore, PVe denotes avertical pitch between neighboring beams through apertures formed at theend portion of the longer axis of the shadow mask, and PVt denotes avertical pitch between adjacent beams through apertures placed at theend portion of the shorter axis of the shadow mask. PVo, PVc, PVe andPVt of the conventional shadow mask have the same value or have adifference of 1˜3% approximately.

The conventional fluorescent screen 4 is formed of R, G, B phosphorsformed on the rear side thereof and arranged in a pattern of a pluralityof stripes or dots and a light absorption material such as a blackcoating 41 formed between neighboring phosphors. An aluminum thin film42 as a conductive layer is formed on the rear side 12 to improve theluminance of the fluorescent screen 4, to protect the fluorescent screen4 from being ion-damaged and to prevent the fall of potential of thefluorescent screen 4.

As for the phosphors R, G and B coated on the screen, as shown in FIG.4, the distance between G and G (or R and R) in the longer axisdirection is called a horizontal pitch SP of the fluorescent screen 4and the distance between G and G (or R and R) in the shorter axisdirection is called a vertical pitch SW thereof.

The vertical pitch PV of the shadow mask 3 has a close relationship withthe moire characteristic, an important characteristic of the CRT, andaffects the purity characteristic and rigidity of the shadow mask 3.

The main factors in the generation of the moire phenomenon in the a CRTincludes the factor affecting the moiré wavelength and the factoraffecting the moire intensity. The factor affecting the moiré wavelengthincludes a scanning line interval of electron beams and the verticalpitch of the shadow mask. The spot size of the electron gun affects themoire intensity. The moiré wavelength is calculated through thefollowing expression.$\lambda = {\frac{1}{\frac{1}{P\; V} - \frac{N}{2\; S}}\mspace{20mu}\lbrack{mm}\rbrack}$

In this expression, S denotes the electron beam scanning line interval,PV denotes the vertical pitch of the beam through apertures and N is aninteger.

The moire intensity is calculated through the following expression$M = {{k( {P\; V} )} \times {\mathbb{e}}^{- \frac{A\; D^{2}N^{2}}{S^{2}}}}$

In this expression, k(PV) denotes a constant determined by PV, A denotesa proportional constant and D is the spot size of the electron beam.

Since moire is the most noticeable when the moire wavelength is 4 mm˜10mm, the vertical pitch of the beam through apertures should bedetermined such that the moire wavelength is not in this range. Inaddition, the higher the moire intensity, the more pronounced the moirephenomenon. Thus, a smaller moire intensity value is preferable.

In case of the CRT, the scanning line interval depends on modes(640×480, 800×600, 1024×768, 1280×1024). Because a variation rate of thevertical pitch of the outer portion of the conventional shadow mask tothat of the central portion thereof is as small as 1%˜3%, it isimpossible to control the vertical pitch so as to make the moirewavelength less than 4 mm by modes.

Furthermore, occurrence of the moire phenomenon can be prevented onlywhen the vertical pitch is controlled according to the electron beamspot size because the spot size depends on positions as shown in theabove expression for calculating the moire intensity. However, this isimpossible with the conventional vertical pitch variation rate.

Moreover, in the relationship among the moire characteristic, puritycharacteristic and shadow mask vertical pitch, the smaller the verticalpitch, the better the moire characteristic. And, the larger the verticalpitch, the better the purity characteristic.

In Korean Patent No. 97-3365, the vertical pitch of the shadow maskincreases as it goes from the central portion to the end portion of theshorter axis of the shadow mask but decreases as it goes from the centerto the end portion of the longer axis of the shadow mask. In KoreanPatent No. 99-27074, the shadow mask vertical pitch increases as it goesfrom the central portion to the skirt portion of the shadow mask.However, the conventional vertical pitches were designed, giving thefirst consideration to the moire characteristic, so that the puritycharacteristic became a problem.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a shadow mask of acolor CRT that substantially obviates one or more problems due tolimitations and disadvantages of the related art.

An object of the present invention is to provide a shadow mask designthat simultaneously satisfies the moire characteristic and puritycharacteristic.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To accomplish the object of the present invention, there is provided acolor cathode-ray tube including a panel having a fluorescent screenformed on the inner surface thereof, a funnel coupled to the panel, anelectron gun mounted into the neck portion of the funnel for emittingelectron beams toward the fluorescent screen, and a shadow mask mountedon the fluorescent screen formed on the inner surface of the panel,having a predetermined distance from the fluorescent screen for carryingout color selection, wherein the shadow mask is a roughly rectangularshape having a longer axis and a shorter axis and including a pluralityof beam through apertures, the vertical pitch of the beam throughapertures being between 0.15 mm and 0.35 mm; and the vertical pitch ofthe beam through apertures increases as it goes from the central portionto the end portion of the shorter axis of the shadow mask.

As a second technical measure to accomplish the object of the invention,there is provided a color cathode-ray tube including a panel having afluorescent screen formed on the inner surface thereof, a funnel coupledto the panel, an electron gun mounted into the neck portion of thefunnel for emitting electron beams toward the fluorescent screen, and ashadow mask mounted on the fluorescent screen formed on the innersurface of the panel and having a predetermined distance from thefluorescent screen for carrying out color selection, wherein the shadowmask is a roughly rectangular shape having a longer axis and a shorteraxis and including a plurality of beam through apertures, the verticalpitch of the beam through apertures being between 0.15 mm and 0.35 mm;and the vertical pitch of the beam through apertures increases as itgoes along the diagonal direction from the central portion to the cornerportion of the shadow mask.

As a third technical measure to achieve the object of the presentinvention, there is provided a color cathode-ray tube including a panelhaving a fluorescent screen formed on the inner surface thereof, afunnel coupled to the panel, an electron gun mounted into the neckportion of the funnel for emitting electron beams toward the fluorescentscreen, and a shadow mask mounted on the fluorescent screen formed onthe inner surface of the panel and having a predetermined distance fromthe fluorescent screen for carrying out color selection, wherein theshadow mask is a roughly rectangular shape having a longer axis and ashorter axis and including a plurality of beam through apertures, thevertical pitch of the beam through apertures being between 0.15 mm and0.35 mm; and the vertical pitch of the beam through apertures formed atthe central portion of the shadow mask is smaller than the verticalpitch of the beam through apertures formed at the end portion of theshorter axis of the shadow mask, the vertical pitch of the beam throughapertures formed at the central portion of the shadow mask being smallerthe vertical pitch of the beam through apertures formed at the cornerportion of the shadow mask.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings;

FIG. 1 is a cross-sectional view of a conventional color CRT;

FIG. 2 illustrates vertical pitches between beam through apertures of ashadow mask;

FIG. 3 illustrates beam through apertures and a fluorescent screen ofthe shadow mask;

FIG. 4 illustrates vertical and horizontal pitches of the fluorescentscreen;

FIG. 5 illustrates an embodiment of a shadow mask structure according tothe present invention; and

FIG. 6 illustrates a horizontal pitch between beam through apertures ofthe shadow mask of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

As shown in FIG. 2, the shadow mask 3 generally has a rectangular formhaving two horizontal longer-axis sides x and two vertical shorter-axissides y. The two horizontal longer-axis sides and two verticalshorter-axis sides are also called longer sides and shorter sides,respectively. The longer sides x are parallel with the central longeraxis of the shadow mask and the shorter sides y are parallel with itsshorter axis.

Furthermore, the shadow mask 3 has beam through apertures 3 a arrangedin vertical rows and horizontal columns. A beam through aperture 3 a ina column and a beam through aperture in a neighboring column are placedin different rows. The vertical distance between neighboring beamthrough apertures in the same row is the vertical pitch PV of the beamthrough apertures and the horizontal distance between adjacent beamthrough apertures in the same row is the horizontal pitch PH of the beamthrough apertures.

The vertical pitch PVo between neighboring beam through apertures formedat the central portion of the shadow mask according to the presentinvention is between 0.15 mm and 0.35 mm and increases as it goes fromthe central portion to the end portion of the shorter axis of the shadowmask.

TABLE 1 Vertical pitch of shadow mask of CRT for 19″ monitor accordingto the present invention Y/X (mm) 0.00 30.00 60.00 90.00 120.00 150.00170.00 177.35 180.00 0.00 0.260 0.260 0.259 0.259 0.258 0.257 0.2560.255 0.255 25.00 0.260 0.260 0.260 0.259 0.258 0.257 0.256 0.256 0.25550.00 0.262 0.262 0.261 0.261 0.260 0.259 0.258 0.257 0.257 75.00 0.2640.264 0.264 0.263 0.262 0.261 0.260 0.260 0.260 100.00 0.268 0.268 0.2670.267 0.266 0.265 0.264 0.264 0.263 125.00 0.274 0.274 0.274 0.274 0.2720.271 0.271 0.270 0.270 133.15 0.276 0.276 0.276 0.275 0.274 0.273 0.2720.272 0.272 135.00 0.276 0.276 0.276 0.275 0.275 0.274 0.273 0.272 0.272

The above table 1 shows the vertical pitch of the shadow mask of a CRTfor a high-resolution 19″ monitor according to an embodiment of thepresent invention. The vertical pitch between beam through apertures ofthe central portion of the shadow mask is 0.2 mm˜0.3 mm.

Referring to FIG. 5, the shadow mask of the present invention isdesigned in a manner that the vertical pitch PVt of beam throughapertures 3 a increases 4%˜12% of the beam through aperture verticalpitch PVo of the central portion of the shadow mask as it goes from thecentral portion to the end portion of the shorter axis of the shadowmask, and the vertical pitch PVc increases 3%˜10%of the vertical pitchof the central portion thereof as it goes from the central portion tothe corner portion of the shadow mask.

Accordingly, when the vertical pitch of the beam through aperturesformed on the central portion of the shadow mask is called PVo, thevertical pitch of the beam through apertures placed at the end portionof the shorter axis thereof is called PVt, and the vertical pitch of thebeam through apertures formed at the corner portion thereof is calledPVc, the following expressions (1) and (2) are satisfied.1.04PVo≦PVt≦1.12PVo  (1)1.03PVo≦PVc≦1.1PVo  (2)

In addition, the vertical pitch PVo of the beam through apertures of thecentral portion of the shadow mask is identical to or larger than 0.2 mmand identical to or smaller than 0.3 mm. If the vertical pitch PVo ofthe central portion of the shadow mask is smaller than 0.2 mm, a spacebetween neighboring apertures of the shadow mask becomes too small. Thiscauses clogging of the mask and increases possibility of generation ofpoor color mixture. Furthermore, purity margin becomes considerablysmall to result in deterioration in ITC productivity. When the verticalpitch PVo is larger than 0.3 mm, the distance between the beam throughapertures 3 a of the shadow mask 3 becomes too large. This decreasesresolution of the color monitor.

When the vertical pitch PVt of the beam through apertures formed at theend portion of the shorter axis of the shadow mask increases less than4% of the vertical pitch of the central portion, ITC productivity isdeteriorated because a space between neighboring apertures of the shadowmask becomes too small as in the case where the vertical pitch issmaller than 0.2 mm. When the vertical pitch PVt of the end portion ofthe shorter axis of the shadow mask increases more than 12% of thevertical pitch of the central portion thereof, resolution is decreasedbecause the distance between the beam through apertures of the shadowmask becomes too large as in the case where the vertical pitch is largerthan 0.3 mm.

The shadow mask is a roughly rectangular shape having longer and shorteraxes and having a plurality of beam through apertures 3 a. The verticalpitch of the beam through apertures 3 a is between 0.15 mm and 0.35 mm.It is preferable that the vertical pitch of the beam through aperturesincreases as it goes from the central portion to the corner portion ofthe shadow mask and the vertical pitch PVc of the beam through aperturesformed at the corner portion of the shadow mask increases 3%˜10% of thevertical pitch PVo of the beam through apertures placed at the centralportion thereof.

When the vertical pitch PVc of the beam through apertures formed at thecorner portion of the shadow mask increases less than 3% or more than10% of the vertical pitch of the central portion of the shadow mask,there occurs the same problem as that occurring when the vertical pitchPVt of the beam through apertures formed at the end portion of theshorter axis of the shadow mask increases less than 4% or more than 12%of the vertical pitch of the central portion of the shadow mask.

Preferably, the vertical pitch PV of the beam through apertures 3 a ofthe shadow mask is formed such that it decreases as it goes from thecenter PVo to the end portion PVe of the longer axis of the shadow mask.

Meanwhile, the horizontal pitch PH of the shadow mask satisfies thefollowing expression (3).0.3 mm≦PH≦0.6 mm  (3)

When the horizontal pitch PH is smaller than 0.3 mm, the distancebetween neighboring beam through apertures 3 a of the shadow maskbecomes narrow to reduce electron beam margin, inversely affectingpurity characteristic. When it is larger than 0.6 mm, the distancebetween the beam through apertures becomes too wide, deteriorating theresolution of the CRT.

Preferably, the horizontal pitch PH of the beam through apertures 3increases as it goes from the central portion PHo to the end portion PHeof the longer axis of the shadow mask.

The electron beams 6 pass through the beam through apertures 3 a of theshadow mask 3 to be scanned on the phosphors R, G and B formed on thescreen. The horizontal pitch SP and vertical pitch SW of the fluorescentscreen depend on the horizontal pitch PH and vertical pitch PV betweenadjacent beam through apertures of the shadow mask. Accordingly, it ispreferable that the relationship between the horizontal pitch SP of thefluorescent screen and the horizontal pitch PH of the beam throughapertures 3 a of the shadow mask satisfies the following expression (4).PH≦SP≦1.1PH  (4)

Furthermore, the vertical pitch PV of the shadow mask according to thepresent invention can be applied to a flat type color CRT including thepanel 1 having an substantially flat outer surface and an curved innersurface, the funnel 2 coupled to the panel 1, the electron gun housedwithin the neck portion of the funnel for emitting the electron beams 6toward the fluorescent screen 4, and the shadow mask 3 formed on theinner surface of the panel having a predetermined distance from thefluorescent screen 4 for carrying out color selection. The shadow maskof the present invention is designed to have the aforementioned verticalpitch so as to prevent occurrence of the moire phenomenon and improvepurity characteristic.

While the conventional beam through apertures 3 a are slot-shaped ordot-shaped, the shape of the beam through apertures of the presentinvention is completely round or close to completely round. Preferably,the vertical pitch Pvo of the beam through apertures 3 a is larger thanor identical to 0.24 mm and smaller than or identical to 0.28 at thecentral portion of the shadow mask.

The forgoing embodiments are merely exemplary and are not to beconstrued as limiting the present invention. The present teachings canbe readily applied to other types of apparatuses. The description of thepresent invention is intended to be illustrative, and not to limit thescope of the claims. Many alternatives, modifications, and variationswill be apparent to those skilled in the art.

According to the present invention, the vertical pitch between adjacentbeam through apertures of the shadow mask increases as it goes from thecentral portion to the end portion of the shorter axis of the shadowmask and it increases as it goes from the central portion to the cornerportion of the shadow mask, thereby satisfying purity characteristic aswell as moire characteristic.

1. A color cathode-ray tube including a panel having a fluorescentscreen formed on the inner surface thereof, a funnel coupled to thepanel, an electron gun mounted into a neck portion of the funnel foremitting electron beams toward the fluorescent screen, and a shadow maskmounted on the fluorescent screen formed on the inner surface of thepanel and having a predetermined distance from the fluorescent screenfor carrying out the color selection, wherein the shadow mask has asubstantially rectangular shape containing a longer axis and a shorteraxis and including a plurality of beam-through apertures and a verticalpitch of the beam-through apertures is between 0.15 mm and 0.35 mm; thevertical pitch of the beam-through apertures increases as it goes from acentral portion to an end portion of the shorter axis of the shadowmask; the vertical pitch of the beam-through apertures formed at thecentral portion of the shadow mask is called PVo, and satisfies thefollowing expression:0.2 mm≦PVo≦0.3 mm; and the vertical pitch of the beam-through aperturesformed at the end portion of the shorter axis of the shadow mask iscalled PVt and the following expression is satisfied:1.04 PVo≦PVt≦1.12 PVo.
 2. The color cathode-ray tube as claimed in claim1, wherein the vertical pitch of the beam-through apertures increases asit goes along the diagonal direction from the central portion to thecorner portion of the shadow mask.
 3. The color cathode-ray tube asclaimed in claim 2, wherein, when the vertical pitch of the beam-throughapertures formed at the corner portion of the shadow mask is called PVcthe following expression is satisfied:1.03 PVo≦PVc≦1.1 PVo.
 4. The color cathode-ray tube as claimed in claim2, wherein when a horizontal pitch of the beam-through apertures iscalled PH, it satisfies the following expression:0.3 mm≦PH≦0.6 mm.
 5. The color cathode-ray tube as claimed in claim 2,wherein a horizontal pitch of the beam-through apertures increases as itgoes from the central portion to the end portion of the longer axis ofthe shadow mask.
 6. The color cathode-ray tube as claimed in claim 5,wherein the horizontal pitch of the beam-through apertures increases asit goes from the central portion to the end portion in the shorter axisdirection or in a diagonal direction.
 7. The color cathode-ray tube asclaimed in claim 2, wherein when a horizontal pitch of a fluorescentmaterial of the screen is called SP and the horizontal pitch of theshadow mask is called PH, they satisfy the following expression:PH≦SP≦1.1 PH.
 8. The color cathode-ray tube as claimed in claim 2,wherein the shape of the beam-through apertures is circular or oval. 9.The color cathode-ray tube as claimed in claim 2, wherein 0.24mm≦PVo≦0.28 mm.
 10. The color cathode-ray tube as claimed in claim 1,wherein the vertical pitch of the beam-through apertures decreases as itgoes from the central portion to the end portion of the longer axis ofthe shadow mask.
 11. The color cathode-ray tube as claimed in claim 1,wherein when a horizontal pitch of the beam-through apertures is calledPH, it satisfies the following expression:0.3 mm≦PH≦0.6 mm.
 12. The color cathode-ray tube as claimed in claim 11,wherein when a horizontal pitch of a fluorescent material of the screenis called SP and the horizontal pitch of the shadow mask is called PH,they satisfy the following expression:PH≦SP≦1.1 PH.
 13. The color cathode-ray tube as claimed in claim 1,wherein a horizontal pitch of the beam-through apertures increases as itgoes from the central portion to the end portion of the longer axis ofthe shadow mask.
 14. The color cathode-ray tube as claimed in claim 13,wherein when a horizontal pitch of the screen is called SP and thehorizontal pitch of the shadow mask is called PH, they satisfy thefollowing expression:PH≦SP≦1.1 PH.
 15. The color cathode-ray tube as claimed in claim 13,wherein the horizontal pitch of the beam-through apertures increases asit goes from the central portion to the end portion in the shorter axisdirection or in a diagonal direction.
 16. The color cathode-ray tube asclaimed in claim 1, wherein when a horizontal pitch of a fluorescentmaterial of the screen is called SP and the horizontal pitch of theshadow mask is called PH, they satisfy the following expression:PH≦SP≦1.1 PH.
 17. The color cathode-ray tube as claimed in claim 1,wherein the panel has a substantially flat outer surface and a curvedinner surface.
 18. The color cathode-ray tube as claimed in claim 1,wherein the shape of the beam-through apertures is circular or oval. 19.The color cathode-ray tube as claimed in claim 1, wherein,0.24 mm≦PVo≦0.28 mm.
 20. A color cathode-ray tube including a panelhaving a fluorescent screen formed on the inner surface thereof, afunnel coupled to the panel, and electron gun mounted into a neckportion of the funnel for emitting electron beams toward the fluorescentscreen, and a shadow mask mounted on the fluorescent screen formed onthe inner surface of the panel and having a predetermined distance fromthe fluorescent screen for carrying out color selection, wherein theshadow mask has a substantially rectangular shape containing a longeraxis and a shorter axis and including a plurality of beam-throughapertures, a vertical pitch of the beam-through apertures is between0.15 mm and 0.35 mm; the vertical pitch of the beam-through aperturesincreases as it goes along a diagonal direction from a central portionto the corner portion of the shadow mask; the vertical pitch of thebeam-through apertures formed at the central portion of the shadow maskis called PVo, and satisfies the following expression:0.2 mm≦PVo≦0.3 mm; and the vertical pitch of the beam-through aperturesformed at corner portion of the shadow mask is called PVc and thefollowing expression is satisfied:1.03 PVo≦PVc≦1.1 PVo.
 21. The color cathode-ray tube as claimed in claim20, wherein the vertical pitch of the beam-through apertures decreasesas it goes from the central portion to the end portion of the longeraxis of the shadow mask.
 22. The color cathode-ray tube as claimed inclaim 20, wherein when a horizontal pitch of the beam-through aperturesis called PH, it satisfies the following expression:0.3 mm≦PH≦0.6 mm.
 23. The color cathode-ray tube as claimed in claim 20,wherein a horizontal pitch of the beam-through apertures increases as itgoes from the central portion to the end portion of the longer axis ofthe shadow mask.
 24. The color cathode-ray tube as claimed in claim 20,wherein when a horizontal pitch of a fluorescent material of the screenis called SP and the horizontal pitch of the shadow mask is called PH,they satisfy the following expression:PH≦SP≦1.1 PH.
 25. The color cathode-ray tube as claimed in claim 20,wherein the panel has a substantially flat outer surface and a curvedinner surface.
 26. The color cathode-ray tube as claimed in claim 20,wherein the shape of the beam-through apertures is circular or oval. 27.The color cathode-ray tube as claimed in claim 20, wherein,0.24 mm≦PVo≦0.28 mm.
 28. A color cathode-ray tube including a panelhaving a fluorescent screen formed on the inner surface thereof, afunnel coupled to the panel, an electron gun mounted into a neck portionof the funnel for emitting electron beams toward the fluorescent screen,and a shadow mask mounted on the fluorescent screen formed on the innersurface of the panel and having a predetermined distance from thefluorescent screen for carrying out the color selection, wherein theshadow mask has a substantially rectangular shape containing a longeraxis and a shorter axis and including a plurality of beam-throughapertures, a vertical pitch of the beam-through apertures being between0.15 mm and 0.35 mm; the vertical pitch of the beam-through aperturesformed at a central portion of the shadow mask is smaller than thevertical pitch of the beam-through apertures formed at an end portion ofthe shorter axis of the shadow mask, the vertical pitch of thebeam-through apertures formed at the central portion of the shadow maskis smaller than the vertical pitch of the beam-through apertures formedat a corner portion of the shadow mask; the vertical pitch of thebeam-through apertures formed at the center portion of the shadow maskis called PVo, and satisfies the following expression:0.2 mm≦PVo≦0.3 mm; and the vertical pitch of the beam-through aperturesformed at the end portion of the shorter axis of the shadow mask iscalled PVt and the following expression is satisfied:1.04 PVo≦PVt≦1.12 PVo.
 29. The color cathode-ray tube as claimed inclaim 28, wherein the vertical pitch of the beam-through aperturesformed at the central portion of the shadow mask is larger than thevertical pitch of the beam-through apertures formed at the end portionof the longer axis of the shadow mask.
 30. The color cathode-ray tube asclaimed in claim 28, wherein the vertical pitch of the beam-throughapertures formed at the end portion of the longer axis of the shadowmask is smaller than the vertical pitch of the beam-through aperturesformed at the corner portion of the shadow mask.